A couple of questions about Bela hardware

giuliomoro

JoelBird The first is simply, what is the pitch of the Bela's pins?

2.54 mm or 0.1 inches

JoelBird The second regards the BeagleBone board: is it possible to access its power and reset switches externally, much like can be done with the Bela button?

The Bela button is connected on P9.27. The PWR button is connected on P9.09. The RESET button should be P9.10, but you shouldn't use that for powering the boards on/off because it won't do a graceful shutdown.

JoelBird

giuliomoro Thanks for the help. Just to clarify, the Bela button does a graceful shutdown, but not either of the BeagleBone buttons? What are the consequences of not doing a graceful shutdown?

giuliomoro

I think this summarises it:

Butto | State  | Tap                       | Hold
--------------------------------------------------------------
Bela  | ON     | Stop/restart Bela program | Graceful shutdown 
      | OFF    | X                         | X
POWER | ON     | Graceful shutdown         | X
      | OFF    | Power on                  | X
RESET | ON     | Hard reset                | X
      | OFF    | X                         | X

A non-graceful shutdown (as the one that occurs with the reset button) is largely equivalent to suddenly removing power. Data loss may occur, but if you didn't access the board via the IDE and edited files and your program is not writing files to disk, that's unlikely to be an issue.

JoelBird

Fantastic, this'll work perfectly for my current project. Now I just need to be able to disable the hold effect of the Bela button, though I'm a little unclear as to how to achieve this just from this webpage [https://learn.bela.io/using-bela/technical-explainers/the-bela-button/]

giuliomoro

you can just run systemctl disable bela_button; systemctl stop bela_button in the console at the bottom of the Bela IDE

JoelBird

Thing is, I'm trying to keep the functionality of the short press intact, if I'm understanding correctly, won't that disable it completely?

giuliomoro

the short press is handled separately inside the Bela program. The bela_button service and bela-cape-btn only handle the hold gesture in the default configuration. This is because the short press can be acted upon much quicker from within the Bela program.

JoelBird

That doesn't seem to have had the right effect, when I do a long press it doesn't fully shut down but it still disconnects from the IDE and behaves unresponsively, with the power LED staying on.

giuliomoro

hmm the commands above should definitely work. Run systemctl status bela_button and show us what it returns

JoelBird

alt text

giuliomoro

so yes it's stopped. You can verify that with ps aux | grep [b]ela-cape-btn which should return nothing .

JoelBird

giuliomoro okay, that function did indeed do nothing. I double checked and it is in fact working as expected. However, the errors I was getting before were using a button wired up to P9.27. Sure enough, using that pin rather than the Bela button itself causes the error. I also noticed that when using the button itself, a short press simply stops the program, but when using the pin, the following errors are generated:
alt text
Am I right in thinking that to use an external button here I just need to bridge P9.27 to ground, or is there more to it?

giuliomoro

So pressing the button should simply stop the current Bela program.

giuliomoro

I think you may be using the wrong pin. You are probably using P9.29 instead of P9.27. Once you get the right pin, shorting it to ground is all you need.

JoelBird

As far as I can tell it's in the right place. In the picture it's the green wire. I've included the wires for I2C SCL (yellow) and SDA (purple) as point of reference.
alt text

giuliomoro

hmm yes that looks like the right one ... is it possible that your cable is very long and its inductance is causing some weird spike in the signal which confuses the nearby McASP bus immediately before triggering the stop of the program? Not sure how that would work electromagnetically ... Try to stick the wire from P9.27 into P9.01 (GND) instead of using your button. Do you get the same result? Where are you taking your ground from? Try adding a 1k series resistor with your button and see if that helps?

It has to be said that regardless of the error message, this seems to be doing what you want: you press the button, the program stops.

JoelBird

Okay, it turns out the issue was on my breadboard. I hadn't realised that the other side of my button was connected up to a completely different part of the circuit, and so was triggering both that and the Bela button. I've now moved it and everything's working correctly, and I feel like a right idiot. Thanks for all the help!